Conventional spiral bevel gears are formed by using a mechanical cutting process. However, such a processing method will waste a lot of material, and requires complicated processing and lengthy processing time, so that the efficiency thereof is low. Moreover, because metal fibers are cut off and are, thus, discontinuous during the cutting process, the structural strength of the finished product is rather weak. Manufacturers mostly use a forging method for pressing and molding. However, because a spiral bevel gear has spiral teeth with a negative draft angle, it cannot be directly stripped from the mold. A cutting tool must be additionally used, thereby resulting in the aforesaid drawbacks of the cutting process.
At present, there are two suggested methods of directly stripping from mold for forging. One method is to use a rotatable punch rod for pushing the processed and completed spiral bevel gear out of the mold. The rotatable punch rod rotates following tooth grooves inside the mold core. However, the punch rod of this method must be provided with a transmission component, such as a gear, and must coordinate with components, such as a motor, a rack bar, or a chain, so that this method is complicated and may destroy the strength of the punch rod. Another method is to rotate the mold core instead of the punch rod so that there is no need to process the punch rod which may destroy the strength thereof. In this method, the mold core is rotated, and the punch rod is used to push the spiral bevel gear out of the mold. Although this method can maintain the strength of the punch rod, the mold core must undergo the process of boring holes and grooves, thereby destroying the strength and the sealing effect of the mold core. Hence, there is still room for improvement.